The general objective of the proposed research is to better understand cardiac biochemistry and the factors which control beating and energy metabolism in the heart. Beating rat heart cells in culture which show age related changes in the beating phenomenon will be used in this proposal. The proposed studies are designed to relate protein biosynthesis with age related events in the life cycle of rat heart cells in culture. Of particular interest is cellular repair, growth (hypertrophy), cell division (hyperplasia), beating, loss of beating, and reinitiation of beating. Protein biosynthesis will be examined several ways including using a labeling procedure with 14C-phenylalanine and 3H-phenylalanine. Each isotope will be added at different times during the life of the cultures. The 14C/3H ratio of fractions obtained from polyacrylamide gel slices will be determined. Specific proteins such as myosin, heavy chains and light chains will be further isolated, purified and characterized. Their properties will be related to the age of the cells in culture and to the state of the beating phenomenon. One specific object of this proposal is to study the biosynthesis, function and structure of cardiac myosin subunits. It is proposed to determine the relationship between the decreased myosin Ca-ATPase specific activity as rat heart cells age in culture and the decreased turnover rate in alkali light chain 1 (LC1) which we have recently seen in cells from older cultures. A second major part of this proposal is to further study lipid involvement in the structure of heart membranes and in energy production. This will require a quantitative and qualitative study of the lipid composition of membranes as a function of age. The preferred fatty acid substrate for beating and the metabolic pathway from medium triglycerides to fatty acids in the mitochondria for energy production will be determined.